Jaguar XK

Feature Article from Hemmings Motor News

Of all the remarkable straight-six engines found under British hoods, from Rolls-Royce and Aston Martin to Triumph and Riley, none has seen longer service or powered a greater number of memorable cars than Jaguar's legendary XK. Yet to call it one of the world's greatest straight-sixes is to sell it short: The XK is simply one of the world's great engines. Period.
Five wins in the 24 Hours of Le Mans would be enough to earn immortality for any engine, but they're just the first line of the XK's resume. Over the six decades it was in production, the XK was the heart of some of the world's most accomplished automobiles-race cars like the C-Type and D-Type, sports cars like the XK-120, XK-140, XK-150 and E-Type, refined sporting saloons like the Mark 2 and S Type, elegant luxury sedans like the Mark VII, Mark X and XJ6, and the car that demands a category all its own, the rare, D Type-based XKSS.
The roots of the XK go back to World War II, when Sir William Lyons, Jaguar's founder, set his engineers to work on an engine to power the new line of cars he intended to introduce once the war ended. The design-the work of chief engineer William Heynes, designer Clyde W.L. Baily, developer W.T.F. "Wally" Hassan and cylinder-head specialist Harry Weslake-was not revolutionary, but it did borrow from the best of pre-war Grand Prix thinking with its aluminum head, chain-driven dual overhead camshafts, aluminum pistons and hemispherical combustion chambers. For strength, the iron crankcase was given seven main bearings. What was revolutionary was that all of this good stuff came in a mass-produced engine priced within reach of the middle class. The name itself, XK, marked it as the eleventh in a series of experimental, or "X," engines that started with the four-cylinder XA.
Jaguar chose a spectacular setting to show off its new gem: the XK-120. At the car's unveiling at the Earls Court motor show in 1948, automotive journalists were skeptical about its claimed 120-mph top speed; their doubts vanished the next year when Jaguar's test driver Ron "Soapy" Sutton covered the flying mile at 132.596 mph on Belgium's Jabbeke Highway. The XK initially had a bore and stroke of 83 x 106mm, for a displacement of 3,442cc, and was capable of producing as much as 210hp at a compression ratio of 8.0:1. A 3.8-liter, 245hp version of the engine was introduced in 1958, followed in 1965 by a 4.2-liter version that produced up to 265hp. Prompted by the energy crises of the 1970s, Jaguar released a destroked, 2.4-liter version that made just 133hp.
Open the hood of an XK-equipped car, and you'll be treated to the sight of those lovely, polished-aluminum cam covers. Lyons, famed for his unerring taste, made certain that the beauty of his cars extended to the engine compartment.
Time finally caught up with the XK. The last Jaguar fitted with the engine, an XJ6, was produced in 1986, and all XK production ended in 1992 when Daimler pulled the plug on its DS420 limousine. It was a remarkable run for a true thoroughbred.

This article originally appeared in the April, 2006 issue of Hemmings Motor News.